1. Field of the Invention
The present invention relates to devices, systems, and processes useful as implantable delivery device, and more specifically to an implantable delivery device which can deliver a drug to a body in two forms having different solubilities for the purpose selecting a desirable release rate.
2. Brief Description of the Related Art
In the area of local drug delivery, such as in drug eluting stents and other implantable drug delivery devices, the control of release kinetics is important to achieving the desired clinical results. For example, it is often desirable to deliver a drug locally over time periods of days, weeks, or longer. It has been found that highly water soluble drugs when coated onto a stent or other implantable device with or without a polymer will be released very fast due to the high water solubility of the drug. Less water soluble drugs are released at a slower rate from similar systems. Often this slower rate is more desirable for local sustained release applications.
The slow or sustained release used in local delivery is generally just the opposite of the desirable release for systemic delivery of a drug by an oral tablet or capsule which requires high water solubility and quick release in a matter of minutes or hours. Accordingly, when a drug intended for oral or other systemic delivery is adapted for local delivery in an implantable medical device, it may be desirable to alter the drug form to achieve a lower solubility and a slower and more sustained release for delivery over many hours and preferably days.
In local drug delivery, either solely the salt (ionic) form of the drug or solely the purely neutral form are delivered. The rate of drug delivery is controlled by the choice of excipient or matrix, but not by the form of the drug. One example of this is in drug eluting stents where the polymer matrices containing the drug are chosen to achieve the desired release kinetic. This often means that non-biodegradable hydrophobic polymers are used to control and slow down the release of the drug.